The present disclosure relates in general to semiconductor devices and their manufacture, and more specifically to the formation of an enriched, high mobility strained SiGe fin having bottom dielectric isolation.
Typical semiconductor devices are formed using active regions of a wafer. The active regions are defined by isolation regions used to separate and electrically isolate adjacent semiconductor devices. For example, in an integrated circuit having a plurality of metal oxide semiconductor field effect transistors (MOSFETs), each MOSFET has a source and a drain that are formed in an active region of a semiconductor layer by implanting n-type or p-type impurities in the layer of semiconductor material. Disposed between the source and the drain is a channel (or body) region. Disposed above the body region is a gate electrode. The gate electrode and the body are spaced apart by a gate dielectric layer.
One particularly advantageous type of MOSFET is known generally as a fin-type field effect transistor (FinFET). The basic electrical layout and the mode of operation of a FinFET does not differ from a traditional field effect transistor. There is one source and one drain contact, as well as a gate to control the source to drain current flow. In contrast to planar MOSFETs, however, the source, drain and channel are built as a three-dimensional bar on top of the semiconductor substrate. The three-dimensional bar is known generally as a “fin,” which serves as the body of the device. The gate electrode is then wrapped over the top and sides of the fin, and the portion of the fin that is under the gate electrode functions as the channel. The source and drain regions are the portions of the fin on either side of the channel that are not under the gate electrode. The dimensions of the fin establish the effective channel length for the transistor.
The use of silicon germanium in semiconductor devices provides desirable device characteristics, including the introduction of strain at the interface between the silicon germanium of the active device and the underlying semiconductor substrate. In general, a strained semiconductor's atoms are stretched beyond their normal inter-atomic distances. As the atoms in the silicon align with the atoms of the silicon germanium (which are arranged a little farther apart, with respect to those of a bulk silicon crystal), the links between the silicon germanium atoms become stretched, thereby leading to strained silicon germanium. Moving atoms farther apart reduces the atomic forces that interfere with the movement of electrons through the silicon germanium, which results in better mobility, better chip performance and lower energy consumption. The faster moving electrons in strained silicon germanium allow faster switching in transistors having strained silicon germanium channel regions.
The strain introduced by using silicon germanium in the active region of a semiconductor device is increased as the concentration of germanium in the silicon germanium increases. However, after growing silicon germanium to a certain level of thickness, defects begin to form, and these defects are proportional to the concentration of germanium in the silicon germanium. Thus, there is generally an inverse relationship between the concentration of germanium in the silicon germanium layer and the thickness to which the silicon germanium layer can be grown without introducing defects.